The present invention relates to cutting utensils and, more particularly, to knives of a type conventionally known as utility knives.
Utility knives are widely used in construction, business and hobby applications for cutting such materials as paper board, wallboard, string, and other objects. In a common embodiment, such utility knives have a handle into which is fitted a trapezoidal blade. The blade has a single cutting edge joining the adjacent edges in acute angles.
As commonly used, such a utility knife includes means for clamping the blade in the handle with one of a portion of the cutting edge and one of the adjacent sides partially exposed whereby cutting is enabled on any part of the exposed edge. In many applications, the portion of the edge at the junction with the acute angle is most used. This portion becomes dulled before the remainder of the blade.
Once the cutting edge revealed in one clamping position becomes dulled, the blade is removed and rotated end for end to place in use the other end of the cutting edge adjacent the opposed acute angle. When the cutting edge at the second end of the blade becomes dulled, the blade is generally discarded and replaced with another blade.
Most utility knives employ a screw or similar means for clamping a single blade in one end thereof with the desired portion revealed. When the revealed edge becomes worn, the screw is removed to release the blade for turning end for end. Such installation and reversal of the blade is time consuming and requires the availability of a screwdriver, or other auxiliary tool.
Prior patents have disclosed knives with a supply of blades in their handles. One such knife, disclosed in U.S. Pat. No. 3,660,896, the disclosure of which is herein incorporated by reference, employs a spring urging a stack of blades from a reservoir into a position where the leading blade can be moved into an operating position. The spring exerts an urging force on the blade stack which varies in accordance with the number of blades in the stack. That is, when several blades are present in the stack, the spring is compressed more tightly and thus exerts a greater force on the stack than when only a single blade is present. The variable force makes the operation of this device less positive than is desirable.
My prior U.S. Pat. No. 4,517,741, the disclosure of which is herein incorporated by reference, solves the variable-force problem of the above reference by employing a permanent magnet in a blade slide facing the blade reservoir. The leading blade in the blade reservoir is attracted into the blade slide with a force dependent upon the strength of the permanent magnet regardless of the number of blades in the reservoir.